The maximum deflection of a row of blades of a turbomachine and thus its aerodynamic load capacity are limited, for one thing, by a separation of the flow along the blade profile. For another thing, the maximum deflection is limited by a separation of a boundary-layer flow on the side walls on the hub side and on the housing side. Double-row blade arrangements are known for purposes of increasing the deflection capacity of rows of blades. A prior-art turbomachine having such an arrangement is shown in FIG. 1. This turbomachine has a hub 2 that is mounted in a housing 4 so as to rotate around a rotor axis 6 that extends in the lengthwise direction x. The hub 2 and the housing 4 delimit an annular main flow path 8 which is traversed from left to right as depicted by the horizontal arrow and in which, for example, a blade-row group 10 on the rotor side, a blade-row group 12 on the stator side and a variable blade-row group 14 are arranged. The blade-row groups 10, 12, 14 each have two rows of blades arranged one after the other in the flow direction, each having a plurality of blades 16, 18. For the sake of clarity, primarily the blade-row group 10 on the rotor side has been provided with reference numerals below. The blade-row group 10 on the rotor side and the blade-row group 12 on the stator side are each firmly joined to the hub 2 and to the housing 4, respectively, whereby a clearance 20 is formed between the tips of the blades 16, 18 and the housing 4 or the hub 2. The blades 16, 18 of the variable blade-row group 14 are each mounted at their ends on a rotary disk 22, 24 and can be pivoted around a transversal axis 26 as depicted by the arrow indicating the rotation. The front blades 16 each have a trailing edge 28 facing the rear blades 18. The rear blades 18 each have a leading edge 30 facing the front blades 16. The edges 28, 30 are configured rectilinearly and they extend radially almost perpendicular to the main flow direction, so that a constant axial edge distance Dconst is formed between the edges 28, 30 and thus between the blades 16, 18. Furthermore, a constant edge distance is formed in the circumferential direction between the edges 28, 30. Moreover, the blades 16, 18 have a constant narrow cross section, a constant degree of overlap on the pressure side, and a constant degree of overlap on the suction side. Moreover, FIG. 1 shows a blade 32 of an individual row of rotor blades.
However, it has been found that, in the side wall area, that is to say, in the area of the hub 2 and/or of the housing 4, the influence of the boundary layer calls for blade contouring that diverges from the center 34 of the main flow path, and by means of this contouring, the flow conditions in the side-wall area that differ from those of the center 34 of the main flow path can be taken into account. Therefore, when it comes to blade-row groups, European patent application EP 2 261 463 A2 proposes to set a meridional distance between the trailing edges of the front blades and the leading edges of the rear blades in such a way that this distance increases from the center of the main flow path in the direction of a side wall on the hub side or housing side.